A storage server is a computer system that is used to store and retrieve data on behalf of one or more clients on a network. A storage server operates on behalf of one or more clients to store and manage data in a set of mass storage devices, such as magnetic or optical storage-based disks or tapes. In conventional network storage systems, the mass storage devices may be organized into one or more groups of drives (e.g., redundant array of inexpensive drives (RAID)).
A storage server may be configured to service file-level requests from clients, as in the case of file servers used in a network attached storage (NAS) environment. Alternatively, a storage server may be configured to service block-level requests from clients, as done by storage servers used in a storage area network (SAN) environment. Further, some storage servers are capable of servicing both file-level and block-level requests, as done by certain storage servers made by NetApp, Inc. of Sunnyvale, Calif.
It is desirable to improve the performance of storage servers, and one way to do so is by reducing the latency associated with accessing stored data. To accomplish this, a storage server may include internal random access memory (RAM) that is used as a buffer cache, to speed up the reading and writing of data from and to (respectively) the main mass storage system. In conventional storage servers, this buffer cache typically is implemented the form of dynamic RAM (DRAM). However, RAM is generally very expensive, so it is prohibitively expensive to equip a storage server with enough RAM to service all of the incoming requests, especially in a large-scale enterprise storage system.